I won't spoil anything don't worry! (and I'll mark spoilers appropriately)
I knew that I would cave in the end and read this!
And you know what??
I'm glad I did.
The contradicting reviews were already in yesterday, with the release of the title. And of course there would be both positive and negative feedback. It's one of the largest franchises out there.
My advice? Ignore them. Just consider that you get one more chance to go back. To Hogwarts, among your beloved characters, plus a bunch of new ones.
Another thing that should be greatly noted is that it is a play. I think the story works better that way, since it reads like fan fiction at times.
Bottomline: If you read this, keep in mind that it's a continuation of the series. So, expect things to change : the trio is all grown up. If you want to leave the story with the echo of the future as described at the end of book 7, then by all means do it. Reading this will put a more definitive way on how things worked out for our cast. Like my title suggests, which is a quote of the book btw, some things will change the way a few characters were in the original books.
(you have been warned: if you don't want to read about the plot/characters do not open the tag)